Detection of resting-state functional connectivity in the lumbar spinal cord with 3T MRI

Abstract

Functional MRI (fMRI) of the spinal cord is an expanding area of research with potential to investigate neuronal activity in the central nervous system. We aimed to characterize the functional connectivity features of the human lumbar spinal cord using resting-state fMRI (rs-fMRI) at 3T, using region-based and data-driven analysis approaches. A 3D multi-shot gradient echo resting-state blood oxygenation level dependent-sensitive rs-fMRI protocol was implemented in 26 healthy participants. Average temporal signal-to-noise ratio in the gray matter was 16.35 ± 4.79 after denoising. Evidence of synchronous signal fluctuations in the ventral and dorsal horns with their contralateral counterparts was observed in representative participants using interactive, exploratory seed-based correlations. Group-wise average in-slice Pearson’s correlations were 0.43 ± 0.17 between ventral horns, and 0.48 ± 0.16 between dorsal horns. Group spatial independent component analysis (ICA) was used to identify areas of coherent activity¸ and revealed components within the gray matter corresponding to anatomical regions. Lower-dimensionality ICA revealed bilateral components corresponding to ventral and dorsal networks. Additional separate ICAs were run on two subsets of the participant group, yielding two sets of components that showed visual consistency and moderate spatial overlap. This work shows feasibility of rs-fMRI to probe the functional features and organization of the lumbar spinal cord.

Lumbosacral spinal cord functional connectivity at rest: From feasibility to reliability

“…A subsequent slice-wise seed-to-voxels analysis, similar to the approach employed by (Barry et al, 2016), further underscored the presence of these bilateral motor networks. This corroborates the findings of Combes and colleagues (Combes et al, 2023), who similarly emphasized substantial connectivity between the ventral horns. However, it is noteworthy that the ventral connectivity reported in their study demonstrated an amplitude more than fourfold stronger than our observations.…”

“…Finally, we did not observe significant connectivity either within (i.e., dorso-ventral) or between (i.e., left dorsal -right ventral and right dorsal -left ventral) hemicords. Such patterns have been observed in the lumbosacral (Combes et al, 2023) and cervical spinal cord (Eippert et al, 2017b;Kaptan et al, 2023;Weber et al, 2018). While these dorso-ventral connections may potentially support polysynaptic spinal reflexes (Sandrini et al, 2005), it is important to emphasize that they seem to be strongly influenced by the specific processing approach (Eippert et al, 2017a;Kaptan et al, 2023) and have exhibited poor reliability (Kaptan et al, 2023).…”

“…However, the reliability of SEEP has been a matter of debate (Bouwman et al, 2008; Jochimsen et al, 2005). Only one recent study capitalized on the BOLD signal within the lumbosacral cord during resting-state scans, providing evidence of discernible patterns of functional connectivity in the spinal cord (Combes et al, 2023).…”

“…This oversight can be attributed, in part, to the challenges associated with fMRI acquisition, processing, and analysis in this region, stemming from the smaller size of the cord (Frostell et al, 2016), heightened anatomical variability (Tins and Balain, 2016; Van Schoor et al, 2015), and the lack of dedicated tools have compounded this difficulty. To date, only one study (Combes et al, 2023) has deployed resting-state fMRI to uncover the intrinsic organization of the lumbosacral spinal cord, shedding light on sensorimotor networks reminiscent of those observed in the cervical spinal cord. Building on these auspicious observations, a critical aspect yet to be explored pertains to the reliability of these lumbosacral functional connectivity patterns.…”

“…To address this knowledge gap, this study sets out to systematically investigate spontaneous BOLD fluctuations in the human lumbosacral spinal cord. Recognizing the susceptibility of spinal cord fMRI to a variety of noise sources, our aims are twofold: firstly, to confirm the presence and nature of organized fluctuations in the lumbosacral spinal cord, employing a sequence distinct from the one used by (Combes et al, 2023); and secondly, to assess the reliability of functional connectivity measures to variations in the denoising procedure. By identifying the optimal approach for assessing functional connectivity in the lumbosacral spinal cord, we intend to contribute to the development of robust methods for studying the functional architecture of this region.…”